Remove duplicate elements from Unsorted array

class Solution
{
    public:
   Node * removeDuplicates( Node *head){
       unordered_set<int> st;
       Node *prev=NULL, *current=head;
       while(current!=NULL){
           if(st.find(current->data)!=st.end()){
               prev->next=current->next;
           }
           else{
               st.insert(current->data);
               prev=current;
           }
           current=current->next;
       }
       return head;
   }
};